1. Field of the Invention
This invention relates to stable water-in-oil emulsions. More particularly, this invention relates to water-in-oil polymer and copolymer emulsions having a water concentration of from about 25 to about 80 by weight based on the total weight of the emulsion which exhibit unusual stability properties.
2. Prior Art
Water-in-oil emulsions of water soluble vinyl addition polymers prepared from water-soluble ethylenically unsaturated monomers have become increasingly important in many areas. These areas include the use of these polymers in the treatment of municipal and industrial wastes, papermaking, as additives to control drift, clarification of aqueous solutions, stabilizers for drilling muds, in the secondary recovery of petroleum by water flooding and in many other applications. Typically, these polymers are made from water-soluble ethylenically unsaturated monomers which include acrylamide, acrylic acid, dimethylaminomethylmethacrylate, methacrylic acid, dimethylaminoethylmethacrylate and methylchloride and dimethyl sulfate quaternary derivatives thereof, dimethyldiallyl ammonium chloride, and other commercially available water soluble vinyl monomers.
For example, Vanderhoff, et al. U.S. Pat. No. 3,184,393 discloses a process for the preparation of water-in-oil emulsions of various water soluble polymers. While Vanderhoff does form an emulsion of various water soluble polymers, the emulsion is not stable, and Vanderhoff must precipitate his polymers as a solid in order to use his process economically.
These Vanderhoff water-soluble polymer systems suffer from several disadvantages. For example, the requirement that the polymers are precipitated as a solid creates additional processing problems. Although these polymers are most often available commercially as powders or as a finely-divided solid, they are most frequently utilized as aqueous solutions. Thus the solid polymer material must be dissolved in water prior to use. Although the various polymers are more or less soluble in water, difficulty is often experienced in preparing aqueous polymer solutions because of their slow dissolution and because the solid polymer is not readily dispersible in water. Furthermore, the dispersion of the solid polymer in water is hindered by its tendency to clump or remain as agglomerates on contact with water. Lumps of the solid polymer immediately form by the encapsulation of undissolved solids in an outer coating of water-wet polymer which retards the penetration of additional water into the agglomerate. Although many of these lumps are eventually dissolved by continued agitation, it is frequently impractical to agitate the solution for a sufficiently long period to obtain complete dissolution.
Several of the disadvantages of the Vanderhoff, et al. patent are allegedly obviated by Anderson, et al. U.S. Pat. No. 3,624,019. Anderson, et al. discloses a method of preparing emulsions of finely divided water soluble polymers prepared from ethylenically unsaturated vinyl addition monomers. The alleged advantage of the Anderson, et al. patent is that the polymer is not isolated in the solid form. Rather, the emulsions are formulated with one or more surfactants which cause them to readily invert into an aqueous solution of the polymer on addition to water. While Anderson, et al. did provide an advancement in the art, these Anderson et al. emulsions have not been as stable as industrial users would like to see in that they often separate into oil and aqueous phases after only a short time. It has been disclosed in the prior art that a part of this instability results from low inverting capabilities of known surfactant systems which mandate that large amounts of the surfactant must be added to the system to provide for inversion within a reasonable period of time after addition to water.
Other disadvantages of the Vanderhoff, et al. patent are alleged obviated by Anderson, et al. U.S. Pat. No. 3,826,771. This patent discloses a water-in-oil emulsion which allegedly exhibits unusual stability properties as compared to the emulsion disclosed in Vanderhoff. The emulsion of the Anderson et al. patent contains an aqueous phase ranging between 75 and 95% by weight of the emulsion. The Anderson et al. patent discloses that the increased water-to-oil ratio of the emulsion as compared to prior art emulsions such as those disclosed in Vanderhoff provides for the improved stability. While the Anderson, et al. emulsion allegedly obviates the stability problem in actual industrial use stability difficulties still persist.
It is therefore an object of this invention to provide a water-in-oil emulsion having improved stability characteristics.
Further objects and advantages of this invention will be apparent from this specification and appended claims.